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JOURNALS // Sibirskie Èlektronnye Matematicheskie Izvestiya [Siberian Electronic Mathematical Reports] // Archive

Sib. Èlektron. Mat. Izv., 2023 Volume 20, Issue 1, Pages 207–210 (Mi semr1581)

Mathematical logic, algebra and number theory

Distance-regular graph with intersection array $\{143,108,27;1,12,117\}$ does not exist

A. A. Makhneva, M. M. Isakovab, A. A. Tokbaevab

a N.N. Krasovskii Institute of Mathematics and Mechanics of the Ural Branch of the Russian Academy of Sciences, str. S.Kovalevskaya, 16, 620990, Yekaterinburg, Russia
b Kabardino-Balkarian State University named after H.M. Berbekov, str. Chernyshevsky, 175, 360004, Nalchik, Russia

Abstract: There is a formally self-dual distance-regular graph $\Gamma$ with classical parameters $d=3$, $b=\alpha+1=q$, $\beta=q^2+q-1$ and intersection array $\{(q^2+q-1)(q^2+q+1),(q^2+q)q^2,q^3;1,(q^2+q),q^2(q^2+q+1)\}$. For the graph $\Gamma$ we have the strongly regular graphs $\Gamma_2$ and $\Gamma_3$ ($\Gamma_3$ is pseuqo-geometric for $pG_{q-1}(q^2+q-1,(q^2+q+1)(q-1))$).
It is proved that a distance-regular graph with intersection array $\{143,108,27;1,12,117\}$ ($q=3$) does not exist.

Keywords: distance-regular graph, formally self-dual graph, triple intersection numbers.

UDC: 519.17

MSC: 05C25

Received October 16, 2021, published March 9, 2023

DOI: 10.33048/semi.2023.20.017



© Steklov Math. Inst. of RAS, 2025